Since in a step of photomechanical process, the formation of sharp dot images or line images is required, an image-forming system showing very high contrast photographic characteristics (in particular, gamma of at least 10). Hitherto, for this purpose, a process of processing a lith-type silver halide photographic material comprising a silver chlorobromide emulsion having a silver chloride content of over 50 mol %, and more preferably over 70 mol % with a specific developer called as a "lithographic developer" containing only hydroquinone as a developing agent and having a very low free sulfite ion concentration (usually not more than 0.1 mol/liter) has been used. However, since for a lith-type silver halide photographic emulsion, a silver chlorobromide having a high silver chloride content must be used, it is difficult to attain a high sensitivity.
As other processes of obtaining high contrast negative images, there are processes using specific hydrazine derivatives disclosed in U.S. Pat. Nos. 4,168,977, 4,224,401, 4,241,164, 4,269,929, 4,311,781, 4,650,746, etc. According to these processes, by processing a surface latent image-type silver halide photographic material containing a specific hydrazine derivative (generally, an acylphenylhydrazine derivative) as a nucleating agent with a developer having pH of from 11.0 to 12.3, photographic characteristics having a superhigh contrast of over 10 in gamma and a high sensitivity are obtained. Since in these processes, a silver bromide emulsion or a silver chlorobromide emulsion having a high silver bromide content can be used, a high sensitivity can be achieved as compared to the case of using lith-type silver halide emulsion.
However, it has been found that the foregoing high contrast image-forming system using the hydrazine derivative has various defects. That is, when the foregoing image-forming system is used, high contrast negative images are obtained but, at the same time, it is accompanied by the formation of pepper (black pepper), which becomes a large problem for a photomechanical process. The pepper in photography means black sesame-like spots occurring in unexposed area, for example, an area to become an undeveloped area between a dot and a dot and the appearance of the pepper causes a trouble of greatly reducing the commercial value as a photographic light-sensitive material for a photomechanical process. Accordingly, various efforts have been made for the development of a pepper restraining technique, but the improvement in pepper susceptibility is frequently accompanied by the reduction of the sensitivity and gamma and, hence, it has been strongly desired to develop an image forming system capable of obtaining a high sensitivity and high contrast without being accompanied by the appearance of the pepper.
A second defect of the conventional high contrast image forming system is that a large amount of expensive hydroquinone must be used for keeping the activity of the developer constant. Since the sulfite ion concentration of the lithographic developer is low, the developer is easily air-oxidized to greatly consume hydroquinone which is the developing agent. In a high contrast image-forming system using a hydrazine derivative, it is allowed to add a sulfite of a high concentration to the developer, but since pH of the developer is high (from 11.0 to 12.3), the developer is liable to be air-oxidized to greatly consume hydroquinone.
Accordingly, for maintaining the developing activity of these developers, it is necessary to use a large amount of expensive hydroquinone or supplement hydroquinone consumed by air-oxidation to maintain the amount of hydroquinone in the developer at above a constant level, and hence the development of a high contrast image-forming system with a developer containing a less amount of hydroquinone or a developer not using hydroquinone as a developing agent has been desired.
On the other hand, a process of obtaining high contrast negative images using a developer containing the compound shown by formula (I) is disclosed in British Patent 2,027,920 but in the process, negative images of a superhigh contrast over 10 in gamma can not be obtained. Also, JP-A-1-130155 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a process of using a dihydroxybenzene derivative developing agent but the process is not for solving the theme of this invention.
As a process of solving such a theme, it was disclosed in Japanese Patent Application No. 2-48022 that by developing an imagewise exposed substantially surface latent image-type silver halide photographic material spectrally sensitized by sensitizing dye(s) with a developer containing at least (1) an aminophenol derivative developing agent and (2) a reductone compound in the existence of at least one kind of a polyalkylene oxide or a derivative thereof, negative images with a very high contrast of over 10 in gamma and with less pepper are obtained. It is an utterly new and astonishing fact that a great increase of sensitivity and superhigh contrast negative images are obtained by the process and conditions disclosed in the aforesaid patent application. Although the detailed mechanism has not yet been clarified, it is considered that a certain high contrast causing reaction occurs in addition to an ordinary development reaction.
However, in the foregoing process, there is a problem that the development requires a substantially long time (e.g., 5 minutes at 20.degree. C.), which is not practical as an image-forming condition.
Thus, as a process of employing a practical development condition, there is a process of adding both of a quaternary ammonium salt and the compound shown by the formula (I) to the developer as disclosed in Japanese Patent Application No. 2-139303 and a process of incorporating a heterocyclic thione compound in a surface latent image-type silver halide photographic material as disclosed in Japanese Patent Application No. 2-178649. In both the processes, negative images having no pepper and a high contrast can be obtained by practical development processing conditions, for example, at 27.degree. C. for 1 minute and 45 seconds. However, when dot images were formed by means of a half tone screen using the foregoing image-forming processes and the dot qualities were comparatively investigated, it has been confirmed that the dot quality by the image-forming processes having improved development conditions is inferior to the dot quality by the image-forming process (Japanese Patent Application No. 2-48022) of processing for a longer development time, and also the development latitude for obtaining good dot images becomes narrower in the former case.